Pulse transmitter circuit for measuring instruments

ABSTRACT

A compact, economically manufactured circuit for generating and transmitting pulses in response to predetermined increments of rotation of an element of a fluid flow meter has a photosensitive component detecting rotation of the meter element. Additional components, including an operational amplifier and logic gates, amplify and shape the signals from the photosensitive component and double the signal frequency to achieve a high pulse frequency capability, uniform pulse shape, good resolution and reliable operation in the presence of severe environmental conditions around the flow meter.

United States Patent 1 Grob [111 3,745,470 [451 July 10,1973

[ PULSE TRANSMITTER CIRCUIT FOR MEASURING INSTRUMENTS [75] Inventor:Russel W. Grob, Metamora, Ill.

[73] Assignee: Caterpillar Tractor Co., Peoria, Ill.

[22] Filed: May 28, 1971 [21] Appl. No.: 147,767

[52] US. Cl 328/38, 328/127, 328/60 [51] Int. Cl, H03]: 5/00 [58] Fieldof Search 328/38, 20, 60-61, 328/74, 127; 307/215 [56] References CitedUNITED STATES PATENTS 3,504,288 3/1970 1 Ross .Q 328/61 3,487,20412/1969 Emmerich 328/ 127 OTHER PUBLICATIONS Marsocci Survey ofSemiconductor Devices pages 31-37 Jan. 1961 Semiconductor Products Vol 4No. 1

Primary Examiner-John W. l-luc-kert Assistant Examiner-R0 E. HartAttorney-Fryer, Tjensvold, Feix, Phillips and Lempio [5 7] ABSTRACT Acompact, economically manufactured circuit for generating andtransmitting pulses in response to predetermined increments of rotationof an element of a fluid flow meter has a photosensitive componentdetecting rotation of the meter element. Additional components,including an operational amplifier and logic gates, amplify and shapethe signals from the photosensitive component and double the signalfrequency to achieve a high pulse frequency capability, uniform pulseshape, good resolution and reliable operation in the presence of severeenvironmental conditions around the flow meter.

5 Claims, 1 Drawing Figure PATENTHJ 3.745.470

INVENTORS RUSSEL W. GROB I ATTORNEYS PULSE TRANSMITTER CIRCUIT FORMEASURING INSTRUMENTS BACKGROUND OF THE INVENTION This invention relatesto measuring instruments of the form providing recurrent electricalpulses indicative of measured data and more particularly to circuits forgenerating the repetitive electrical pulses which represent the datameasured by an instrument of this form.

Many instruments for monitoring a physical phenomenon produce a seriesof electrical pulses in order to transmit the detected information to arecording device, or digital data processing system or the like. Onespecific example of such an instrument is described in co-pendingapplication Ser. No. 135,300 of Albert B. Niles et al. for Method andApparatus for Checking Engine Performance, filed Apr. 19, 1971 andassigned to the Assignee of the present application. This copendingapplication describes apparatus for determining the power output, interms of brake horsepower or the like, of an internal combustion engine.Power output of the engine is determined in part from electrical signalsgenerated at a volume measuring flow meter connected into the fuel linesof the engine under test. To provide accurate power computations, thedegitizing flow meter must reliably produce a uniform output pulse inresponse to each predetermined incrementof rotation of an element of themeter which is turned by the fuel flow therethrough. These outputpulses, in the meter of the co-pending application, are initiated bypassage of radial slits in a rotating disc across the optical pathbetween a light source and a photosensitive element.

In the above described instrument as well as in many others, it may bedesirable that output pulses be produced at a frequency greater than therate of recurrenceof the events which initiate the output pulses. In theparticular example discussed above, mechanical factors limit the numberof radial slits which can be provided in the disc to a value less thanthe number of output pulses which are desired for each revolution of thedisc. Accordingly the output pulse generating circuit should be capableof multiplying pulse frequency. To provide maximum accuracy andreliability still other conditions must be met. Output pulses shouldhave a uniform wave shape and amplitude which are not sensitive tovariations in the characteristics of the event which initiates thepulses. In the example discussed above such variations may result fromdifferences in speed of rotation or because of inconsistencies in slitwidth and changing optical distance of the slit, due to irregularmovements of the rotating disc, between the light source andphotosensitive element, causing the element's output to vary. Further,the pulse generating circuit may be physically associated with themeasuring instrument rather than the remote data processing equipmentand thus may be subjected to difficult environmental factors. In thespecific example discussed above, the flow meter including the pulsegenerating circuit is attached to an operating engine and thus mustoperate reliably in thepresence of high temperatures, severe temperaturefluctuations and vibration.

Prior circuits for performing a similar function have not met thesecriteria to the desired degree either in the specific context discussedabove for purposes of example or in conjunction with other measuringoperations wherein repetitive pulse signals are required from ameasuring instrument.

SUMMARY OF THE INVENTION pulses in response to successive increments ofa measured quantity wherein output pulse frequency is multipliedrelative to the rate of occurrence of events which initiate the outputpulses. In a preferred form, the invention uses a photosensitivecomponent to sense movement of an element of a measuring instrument andthe signal from the photosensitive component is interpreted, amplified,increased in frequency and transmitted by circuit means including anoperational amplifier and logic gates in a novel arrangement having theproperties discussed above.

Accordingly it is an object of this invention to facilitate the couplingof data recording or processing devices to measuring instruments whichprovide input data therefor.

The invention, together with further objects and advantages thereof,will best be understood by reference to the following description of apreferred embodiment and by reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is a schematicdiagram of an exemplary embodiment of the pulse generating andtransmitting circuit as associated with a fluid flow meter which isshown diagramatically in the drawing.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawing, theflow meter 11 with which pulse transmitting circuit 12 is associated inthis example of the invention may be of known construction andaccordingly is shown only diagramatically in the drawing. Such a meter11 may consist essentially of a rotary fluid motor 13 connected into aflow conduit 14 whereby the motor isturned by the fluid flow at a rateproportional to the magnitude of the flow. In one common form ofdigitizing flow meter 11 the motor 13 turns a disc 16 having a series ofequiangularly spaced radial slots 17. Transducer means are provided togenerate an electrical signal indicative of the amount of rotation ofmotor 13 and disc 16 and thus indicative of the amount of fluid whichpasses through the meter. The transducer may consist of a light source18 disposed at one side of disc 16 and a photosensitive component suchas a phototransistor 19 situated at the opposite side of the disc toreceive light transmitted through the slits 17. Thus the light intensityreaching phototransistor 19 increases momentarily each time that a slit17 passes across the optical path between the source 18 and thephototransistor.

To energize the light source 181, phototransistor 19 and elements ofpulse transmitting circuit 12, with constant operating voltages, a powersupply circuit 21 is provided. Power supply circuit 21 includes apositive DC power input terminal 22 and grounded negative terminal 23for connection to a suitable unregulated DC power supply which may, forexample, be a remotely situated battery 24 connected across terminals 22and 23 in series with a control switch 26. Operating power for pulsetransmitting circuit 12 is supplied to a 8+ conductor 27 thereof througha resistor 28 which connects conductor 27 to terminal 22. To energizelight source 18, one terminal of the source is grounded while the otherconnects to power supply terminal 22 through a pair of series resistors29 and 31. To assure that a constant DC voltage is applied to 13+conductor 27 a zener diode 32 is connected between the B+ conductor andnegative power supply terminal 23. To assure that a constant lowervoltage is provided for the light source 18, a second zener diode 33 isconnected between the junction of resistors 29 and 31 and terminal 23.Resistors 29 and 31 serve to provide a lower voltage to light source 18than is provided to the pulse circuit B+ conductor 27 inasmuch as inthis example the light source is designed to operate with less votagethan certain components in the pulse transmitter circuit.

To energize the phototransistor 19, the emitter thereof is connected toa circuit ground conductor 34 while the collector of the phototransistorconnects to 8+ conductor 27 through a dropping resistor 36. Conductivitythrough the phototransistor 19 is a function of the intensity of theambient light and accordingly the voltage at the collector of thephototransistor drops momentarily each time that a slit 17 of disc 16passes between light source 18 and the phototransistor.

The major functions of the pulse transmitting circuit 12 are to detect,amplify, multiply, shape and transmit the collector signals atphototransistor 19 which result from rotation of disc 16. For thispurpose, the voltage fluctuations at the collector of phototransistor 19are coupled to the input signal terminal 37 of an operational amplifier38 through a capacitor 39. Thus the voltage at input terminal 37 ofoperational amplifier 38 drops momentarily each time a slit of disc 16crosses the optical path between light source 18 and the phototransistor19 as illustrated by wave shape 37' in the drawing. During each suchdrop the voltage passes through a reference .voltage value which isvolts in this instance. Operational amplifier 38 is connected tofunction as a zero crossing detector to respond to the momentary voltagedrops at terminal 37 by producing amplified positive substantiallysquare wave pulses ranging from 0 to volts, as indicated by wave shape38 in the drawing. For this purpose the positive and negative powerterminals of operational amplifier 38 are connected to conductors 27 and34 respectively and a fixed reference voltage of 5 volts, in thisinstance, is established at the other amplifier input terminal 43. Toprovide the reference voltage, a resistor 44 and zener diode 46 areconnected in series between B+ conductor 27 and ground conductor 34 andin accordance with the well known action of a zener diode, the desiredfixed potential is maintained at the junction between the diode and theresistor 44. Such junction is connected to the reference input 43 ofamplifier 38 through a resistor 47 and is connected to input 37 througha resistor 48. Thus in the absence of a voltage change atphototransistor 19, the same potential is present at both inputs of theamplifier and no signal is present at the output 49 thereof. Whencapacitor 39 transmits a voltage drop at the phototransistor 19 to input37, the potential at input 37 momentarily fluctuates with respect to thepotential at reference input 43 and an amplified output pulse isproduced at output 49. To supress transient voltage fluctuations atamplifier input 43 a capacitor 51 is connected across the terminals ofzener diode 46.

Accordingly as successive ones of the slits 17 of disc 16 sweep past theoptical path between the light source 18 and phototransistor 19 asequence of square wave pulses is generated at the output 49 ofoperational amplifier 38 at a frequency proportional to the speed ofrotation of the disc. In order to provide for increased accuracy andresolution in digital data processing circuits with which this systemmay be used, means are provided for doubling the frequency of suchoutput pulses 38' prior to transmission to the associated pulseutilizing circuits. Accordingly the output of amplifier 38 is coupled toa flow signal transmitting terminal 52 through a frequency doublingmeans. For this purpose an output NAND gate 53 has an output coupled toterminal 52 and has first and second inputs coupled to B+ conductor 27through similar resistors 54 and 56. respectively. Thus when theamplifier 38 output is not affecting the output gate 53 as willhereinafter be described, equal potentials are present at both inputs ofthe gate and in accordance with the well known operation of a NAND gateno signal is present at the output thereof. To cause gate 53 to generatetwo discrete uniform square wave pulses for each pulse from the outputof amplifier 38, the amplifier output conductor 49 is branched toconnect with one input each of a second and third NAND gate 57 and 58.The output of NAND gate 57 is connected through a capacitor 59 to oneinput of gate 53 while the output of gate 58 is connected to the otherinput of gate 53 through a fourth NAND gate 61 and capacitor 62.

The NAND gates 57, 58 and 61 are here used to function essentially asinverters and accordingly the other inputs to each of these three NANDgates are connected to B+ conductor 27. With one input permanently higha NAND gate acts simply to invert signals applied to the other input.NAND gates are used to providethe inversion function in part sincecompact integrated circuit elements are available which embody four NANDgates. This is simpler and less costly than a circuit including anindividual NAND gate 53 and three discrete inverters. Moreover, as willbecome evident from the description of the operation of the frequencydoubling portion of the circuit, the structural similarity of the fourelements 53, 57, 61 and 58 assures production of uniformly shaped andspaced output pulses as required for optimum operation of associateddigital circuits or the like.

In the absence of an output signal from amplifier 38, both inputs ofNAND gate 53 are at equal voltages and the output of NAND gate 53 istherefore low. The output of NAND gate 57 is high while the output ofNAND gate 61 is low but owing to the presense of capacitors 59 and 62these signals do not affect NAND gate 53 as long as there is no changein such signals. When an output pulse 38' is produced by amplifier 38,the leading edge of such pulse causes the output of NAND gate 57 to dropto a low condition while the output of NAND gate 61 is caused to rise toa high condition owing to the inverting action of the several NAND gates57, 58 and 61. Capacitor 59 and resistor 56 is conjunction and capacitor62 and resistor 54 in conjunction each act as a differentiator causingthe voltage changes at the outputs of NAND gates 57 and 61 respectivelyto be applied to one input of NAND gate 53 as a positive voltage spikewhile simultaneously applying a negative voltage spike to the otherinput of NAND gate 53. Accordingly, the output of NAND gate 53 brieflygoes high to produce a first substantially square wave brief outputpulse at transmitting terminal 52. Subsequently, when the trailing edgeof the amplifier output pulse 38' occurs, the outputs of NAND gates 57and 61 revert to the original condition. Through the differentiatingaction of the capacitors 59 and 62 and resistors 54 and 56 this againapplies brief oppositely directed voltage spikes to the two inputs ofNAND gate 53 causing a second output pulse at transmitting terminal 52.

Accordingly each output pulse from amplifier 38 produces a pair ofdiscrete sequential circuit output pulses at transmitting terminals 52to achieve the desired multiplying of the original frequency. Moreoveras the output pulses at terminal 52 are derived through enabling anddisabling of the NAND gate 53, such pulses are highly uniform, distinctand of a substantially square wave configuration. It will be apparentthat if multiplication of the original frequency by a factor greaterthan two is desired, essentially similar stages of the frequencydoubling portion of the circuit may be connected in tandem betweenamplifier 38 and transmitting terminal 52 as necessary.

While it might appear at first consideration that the passage ofamplifier 38 output pulses through first one inverting device and thenanother, specifically NAND gates 58 and 61 in this example would ineffect restore the pulses to the original condition making the presenceof gates 58 and 61 seemingly redundant, this is not the case inpractice. Pulses in one branch of the output of amplifier 38 areinverted in passing through gate 58 and if the pulses in the otherbranch were passed directly from amplifier output 49 to capacitor 62there might be an imbalance in the shape of the voltage spikes appliedto the two-capacitors 59 and 62. Thus signals to both of capacitors 59and 62 are passed through a NAND gate and since the signals in one pathshould be inverted relative to those in the others, one of the paths isprovided with two inverting gates. This aids significantly in realizingthe desired objective of uniform output pulses at terminal 52 and inachieving reliable and accurate response at high pulse frequen cies.

Accordingly pulses generated by phototransistor 19 are detected,amplified and optimally shaped and applied to signal output terminal 52at twice the original frequency. Terminal 52, which is paired with aground terminal 63 so that the pulse transmitter circuit ground may bematched with that of remote signal utilizing apparatus, may be coupledby suitable conductors with any ,recording or data processing systemrequiring pulsed input signals having a frequency indicative of the rateof fluid flow through conduit 14. The engine horsepower readoutapparatus described in co-pending application Ser. No. 135,300,previously referred to describes one such data processing system.

While the invention has been described with respect to a singlepreferred embodiment, it will be apparent that numerous modificationsare possible and it is not intended to limit the invention except asdefined by the following claims.

What is claimed is: t

1. A pulse generating and transmitting circuit for re sponding to arecurrent phenomenon by producing electrical output pulses at afrequency greater than that of said recurrent phenomenon comprising:

transducer means for detecting said phenomenon and for producing anelectrical signal in response to each recurrence thereof,

an amplifier having an input coupled to said transducer means forreceiving said signals therefrom and having an output at which anamplified pulse is generated in response to each of said signals,

an output NAND gate means of the form having a pair of inputs and havingan output at which a substantially square wave pulse is produced inresponse to an imbalance of electrical potential at said inputs and atwhich no pulse is produced when equal electrical potentials are presentat'each of said inputs,

first and second differentiating circuits each being connected betweensaid amplifier output and a separate one of said inputs of said outputgate means to define a pair of separate pulse paths between saidamplifier output and said output gate means, and

means coupled to one of said pulse paths between said differentiatingcircuit thereof and said amplifier for inverting pulses transmitted tosaid output gate means through said one pulse path relative to pulsestransmitted to said output gate means through said other pulse path,

whereby said output gate means produces a pair of output pulses ofreduced duration for each output pulse from said amplifier.

2. A circuit as defined in claim 1 wherein said amplifier is anoperational amplifier having an input signal terminal receiving saidsignals from said transducer means and having a reference input to whicha fixed voltage is applied which fixed voltage is intermediate betweenthe voltage extremes of said signals from said transducer means andwherein said amplifier output undergoes a transition from a firstvoltage level to a second voltage level in response to each change ofpotential at said input terminal through said fixed refer ence voltagelevel.

3. A circuit as defined in claim 1 further comprising a DC power supplyand wherein each of said first said second differentiating circuitscomprises a resistor connected between a single terminal of said powersupply and the associated one of said inputs of said output gate meansand further comprises a capacitor connected between said associatedinput of said output gate means and said amplifier output whereby saidpower supply normally provides equal potentials to said inputs of saidoutput gate means, the potential at one of said inputs of said outputgate means being momentarily changed from the potential at the otherthereof by the leading edge of each output pulse from said amplifier asreceived through one of said two pulse paths and the potential at saidother of said inputs being momentarily changed from the potential atsaid one thereof by the trailing edge of said amplifier output pulse.

4. A circuit as defined in claim 1 wherein said means for invertingpulses in one of said pulse paths relative to pulses in the otherthereof comprises a first signal inverting means connected into one ofsaid pulse paths and a pair of signal inverting means connected into theother of said pulse paths in series relationship whereby pulses in saidother pulse paths are twice inverted whereas pulses in said first pulsepath are inverted once said first signal inverting means and said pairof signal inverting means all being substantialy identical.

5. A circuit as defined in claim 4 wherein each of said signal invertingmeans are NAND gates substantially identical to said NAND gate outputmeans.

1. A pulse generating and transmitting circuit for responding to arecurrent phenomenon by producing electrical output pulses at afrequency greater than that of said recurrent phenomenon comprising:transducer means for detecting said phenomenon and for producing anelectrical signal in response to each recurrence thereof, an amplifierhaving an input coupled to said transducer means for receiving saidsignals therefrom and having an output at which an amplified pulse isgenerated in response to each of said signals, an output NAND gate meansof the form having a pair of inputs and having an output at which asubstantially square wave pulse is produced in response to an imbalanceof electrical potential at said inputs and at which no pulse is producedwhen equal electrical potentials are present at each of said inputs,first and second differentiating circuits each being connected betweensaid amplifier output and a separate one of said inputs of said outputgate means to define a pair of separate pulse paths between saidamplifier output and said output gate means, and means coupled to one ofsaid pulse paths between said differentiating circuit thereof and saidamplifier for inverting pulses transmitted to said output gate meansthrough said one pulse path relative to pulses transmitted to saidoutput gate means through said other pulse path, whereby said outputgate means produces a pair of output pulses of reduced duration for eachoutput pulse from said amplifier.
 2. A circuit as defined in claim 1wherein said amplifier is an operational amplifier having an inputsignal terminal receiving said signals from said transducer means andhaving a reference input to which a fixed voltage is applied which fixedvoltage is intermediate between the voltage extremes of said signalsfrom said transducer means and wherein said amplifier output undergoes atransition from a first voltage level to a second voltage level inresponse to each change of potential at said input terminal through saidfixed reference voltage level.
 3. A circuit as defined in claim 1further comprising a DC power supply and wherein each of said first saidsecond differentiating circuits comprises a resistor connected between asingle terminal of said power supply and the associated one of saidinputs of said output gate means and further comprises a capacitorconnected between said associated input of said output gate means andsaid amplifier output whereby said power supply normally provides equalpotentials to said inputs of said output gate means, the potential atone of said inputs of said output gate means being momentarily changedfrom the potential at the other thereof by the leading edge of eachoutput pulse from said amplifier as received through one of said twopulse paths and the potential at said other of said inputs beingmomentarily changed from the potential at said one thereof by thetrailing edge of said amplifier output pulse.
 4. A circuit as defined inclaim 1 wherein said means for inverting pulses in one of said pulsepaths relative to pulses in the other thereof comprises a first signalinverting means connected into one of said pulse paths and a pair ofsignal inverting means connected into the other of said pulse paths inseries relationship whereby pulses in said other pulse paths are twiceinverted whereas pulses in said first pulse path are inverted once saidfirst signal inverting means and said pair of signal inverting means allbeing substantial y identical.
 5. A circuit as defined in claim 4wherein each of said signal inverting means are NAND gates substantiallyidentical to said NAND gate output means.